The gunman who shot a student at a high school in Colorado last week had letters and numbers written in permanent marker on his arm indicating that he planned to target several areas inside the school, the authorities said Tuesday.

The gunman, Karl H. Pierson, 18, killed himself after opening fire at Arapahoe High School in Centennial, Colo., a suburb of Denver, on Friday.

He fired a shotgun inside the school five times and seriously wounded a student, Claire Davis, 17.

The five letters and numbers on Pierson’s forearm were linked to the locations of the school’s library and several classrooms, showing which areas he planned to attack, the Arapahoe County Sheriff’s Office said.

The sheriff’s office is investigating whether the gunman was targeting teachers or students in those classrooms.

Pierson also had the Latin phrase “Alea iacta est” written on his arm. It means “The die has been cast.”

The authorities have said Pierson, a student at the school, planned to confront a teacher and was armed with enough weapons to hurt many others.

In addition to the shotgun, he had three gasoline bombs, a machete and 125 rounds of ammunition, the sheriff’s office said.

Davis, a senior at the school, remained in a coma Tuesday, according to The Denver Post. She was seated near an entrance to the school and was not a planned target, the authorities have said.